Continuous ion exchange (CIX) processes have been previously presented for recovery rather than purification of cobalt from hydrometallurgical process solution, described for example in WO 2011/100442 and WO 2013/165735. These inventions depict a continuous cross current/partial counter current ion exchange procedure such as described in Bailey et al., Removal of Nickel from Cobalt Sulfate Electrolyte Using ISEPTM Continuous Ion Exchange; in Proceedings of Copper, Cobalt, Nickel and Zinc recovery, International conference, Victoria Falls, Zimbabwe, 16-18 Jul. 2001, SAIMM, Johannesburg. The requirements for cobalt recovery in the aforementioned inventions are in general:
(i) The ion exchange material used has high affinity and sufficient capacity for cobalt.
(ii) Cobalt concentration in the hydrometallurgical process solution treated is low, in the examples presented in the aforementioned inventions preferably less than 0.5 g/L.
The present invention pertains to purification rather than recovery of concentrated cobalt sulfate hydrometallurgical process solutions containing cobalt from 10 g/L to saturated solution. The ion exchange materials presented in the aforementioned inventions, specifically bis-2-(pyridylmethyl)amine (also known as bis-picolylamine) functionalized ion exchange resins, are incapable of recovering cobalt from solutions of significantly high Co concentration (see reference example 3).
The method described in the present invention uses counter current simulated moving bed (SMB) continuous ion exchange (CIX) in a thus far unutilized arrangement to purify cobalt from impurity metals. SMB chromatography has been used to separate acid and metals from a hydrometallurgical process solution (US 2008/0093302) in the traditional SMB arrangement. Briefly, in such an SMB process the stronger adsorbing components are carried by the solid phase (ion exchange resin) counter current to the less adsorbing components carried downstream by the liquid and collected in their respective outlets either upstream or downstream from the feed port. Examples of fully continuous SMB processes where each step is identical can be found in U.S. Pat. No. 4,182,633 and U.S. Pat. No. 4,412,866. Time variable or non-identical step SMB processes are described for example in U.S. Pat. No. 5,064,539 and U.S. Pat. No. 5,102,553. SMB may also be operated semi-continuously or sequentially as described for example in U.S. Pat. No. 5,127,957.
In relation to previously published cobalt recovery and purification from sulfate solutions using continuous ion exchange the novelty of the present invention pertains to:
1) Treating solutions where cobalt is the primary component, present in concentrations from 10 g/L to saturated solution.
2) Using continuous ion exchange in simulated moving bed in a manner not previously published for cobalt recovery and purification, specifically eluting the target metal with mineral acid to produce a Co rich front to raffinate, while impurities are adsorbed to the resin of a bed, transported counter-current to the Co-solution being treated, and then desorbed from the resin of said bed in a separate zone upstream from the bed into which present Co containing feed solution is fed.3) Generally combining features of counter current SMB chromatography, known mainly in pharmaceuticals and sweeteners production and also described for acid/metal separation in US 2008/0093302, with cross current open circuit continuous ion exchange such as described in WO 2011/100442 and WO 2013/165735, in recovery and separation of metals from impurity metals from hydrometallurgical process solutions.
Metals recovery by sequential multi-column ion exchange system has also been presented in US 2010/0326918. The invention presented therein pertains to ionic metal complexes of for example Co that may be either the most retained or the least retained component by the ion exchange material. The process described in US 2010/0326918 functions by cross current zones and does not feature a counter current elution such as depicted in the present invention. Further no examples to cobalt purification are presented in the aforementioned invention.